Fine-structural changes of the synovial membrane in arthrosis deformans

Repair of partial-thickness defects in articular cartilage: cell recruitment from the synovial membrane

Partial-thickness defects evolving in mature articular cartilage do not heal spontaneously. This type of defect was created in the articular cartilage of adult rabbits and Yucatan minipigs, and the effects of chondroitinase ABC or trypsin, fibrin clots, and mitogenic growth factors on the healing process were examined histologically at intervals ranging from one to forty-eight weeks. The effect of chondroitinase ABC or trypsin was examined initially. Articular cartilage contains macromolecules, including proteoglycans, which render the surfaces of this tissue, and of partial-thickness defects within it, antiadhesive. Chondroitinase ABC digests the glycosaminoglycan chains of cartilage proteoglycans, and trypsin degrades their core proteins. To test the hypothesis that mesenchymal cells may be prevented from adhering to and migrating over the surfaces of partial-thickness defects by proteoglycans, we removed a superficial layer of these macromolecules from the surface of the defect with use of one of these enzymes. The treatment evoked an increase in the coverage of the defect surface with mesenchymal cells; when combined with the local application of a mitogenic growth factor (basic fibroblast growth factor, transforming growth factor-beta 1, epidermal growth factor, insulin-like growth factor-1, or growth hormone), the coverage was more extensive but mesenchymal cells did not extend into and completely fill the volume of the defect. When the surface of the defect was treated with chondroitinase ABC and the cavity of the defect was filled with a fibrin clot to furnish a matrix or scaffolding for the migration of cells therein, there was migration and proliferation of cells throughout the volume of the defect but at a low population density. Mesenchymal cells remodeled the deposited fibrin matrix, which was replaced by a loose fibrous connective tissue. When defects that had been treated with chondroitinase ABC were filled with a fibrin clot containing a mitogenic growth factor, mesenchymal cells filled the entire cavity of the defect, and the density of the cells was greatly increased, particularly when transforming growth factor-beta 1 was used. Histological studies revealed a continuous layer of mesenchymal cells extending from the synovial membrane across the superficial tangential zone of normal articular cartilage into the defect, indicating that the cells that were recruited for the repair process were of synovial origin. At forty-eight weeks, the entire cavity of the defect remained filled with a fibrous connective tissue.

The uptake of horseradish peroxidase in monkey temporomandibular joint synovium after occlusal alteration

We conducted an electron microscopic study on the alterations in the temporomandibular joint (TMJ) synovium of the monkey after it was subjected to unilateral bite-raising, by means of a maxillary occlusal splint. The uptake of intravenously injected horseradish peroxidase (HRP) by type A cells was demonstrated in the disturbed TMJ. The uptake of HRP decreased three to six wk after occlusal alteration, and was the same as in normal type A synovial cells after 16 wk.

The uptake of horseradish peroxidase in the temporomandibular joint synovium of the rat following unilateral extraction of molars

Unilateral extraction of rat molars was followed by degeneration of type A temporomandibular joint synovial lining cells. The uptake of intravenously injected HRP decreased in accordance with the degree of degenerative change. Normal passage of proteins from blood to joint cavity appears to be controlled by the synovium, especially by type A cells. This study suggests that, with certain TMJ disturbances, control of protein transport may be altered.

Epithelioid sarcoma: ultrastructural similarity to nodular synovitis

The ultrastructure of nodular synovitis of the knee and epithelioid sarcoma of the hand are compared. Both lesions show a similar pattern of light and dark cells having filopodia and microvilli, an outer coat of finely granular matrix without well defined basal laminae, maculae adherentes and attachment sites, pinocytotic vesicles, cytoplasmic filaments and complex nuclear invaginations. These similarities suggest a common histogenesis and support the concept that the epithelioid sarcoma is derived from synovioblastic mesenchyme.